Titanium alloys have been widely used in making components for aircraft, medical implants and chemical processing machinery and structures.
Titanium alloys can also be used to replace steel in making automotive components, but this application has been severely limited by the cost issues. This high cost is largely a result of expensive batch processes that are used to recover titanium from its mineral concentrates, and the technical difficulties associated with melting and alloying titanium.
The conventional titanium production process, the Kroll process, involves the reaction of TiO2 and carbon, in the form of coke, under chlorine gas at temperatures of 800° C. to form TiCl4 and carbon monoxide.
The titanium chloride (TiCl4) produced in the reaction exists as a liquid and has to be purified by distillation. The liquid is introduced into a furnace holding a magnesium melt at 680° C. to 750° C. to facilitate the formation of magnesium chloride (MgCl2) and pure titanium. MgCl2 is a gas, while titanium is a solid sponge. The sponge is purified by distillation or leaching using hydrochloric acid. The magnesium chloride can be recycled through an electrolysis process. The titanium sponge that is formed by this process can then be further processed to produce commercial purity titanium or titanium alloys by vacuum arc melting or other such melting methods.
If titanium or titanium alloy powder is needed, the titanium or titanium alloys need to be heated to a high temperature above (1650° C.) to produce titanium/alloy melt. This is atomized into liquid droplets which in turn solidifies as powders.
The limitations of this process include its complexity and the use of chlorine and magnesium. The process involves several high temperature steps where a high amount of energy is needed. This contributes to the high cost of titanium and titanium alloys. The use of chlorine makes the process environmentally unfriendly. Magnesium metal is expensive, so the use of magnesium in the process also contributes to the high cost of titanium. The result of this process is that the cost of the titanium alloy powder is in the range of US $40 per kilogram.
U.S. Pat. No. 6,264,719 (Zhang et al.) discloses both a titanium alloy based dispersion-strengthened composite and a method of manufacture of the same. This patent discloses the use of dry high-energy intensive mechanical milling in the process of producing titanium based metal matrix composites (MMC).
MMCs are composites of a tough conventional engineering alloy and a high strength second phase material, which may be an oxide, nitride, carbide or intermetallic. Oxide Dispersion Strengthened (ODS) alloys occur at one end of the spectrum of MMCs. These are composites of a tough engineering alloy and a fine dispersion of an oxide. Typically, in order to obtain the required dispersion, there must be no more than 10% volume fraction of the oxide second phase, which may have a size of 10's of nm.
While U.S. Pat. No. 6,264,719 discloses a method of producing titanium based MMCs at a reduced cost, it does not disclose a method for separating out the unwanted components within the MMC, thus adjusting the level of certain components in the composite to more desirable concentration. The ability to use such a process to recover metal components including metals other than Ti would also be an advantage.
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It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more of the steps in a method or process.